Excessive gastric acidity and mental stress were earlier thought to be major pathophysiological reasons for occurrence of peptic ulcers. Marshall and Warren (Warren., Lancet, 1: 1273-1275, 1983 and Marshall etal., Lancet, 2: 1311-1315, 1984) first reported an unidentified curved bacilli in the stomach of patients with gastric and peptic ulcers. These bacilli which were later identified as a gram negative spiral bacterium and named Helicobactor pylori (Goodwin et al., Int. J. Syst. Bacteriol. 39: 397-405, 1989), have been demonstrated to be associated with gastric and peptic ulcers (Buck et al., J. Infect. Dis. 153: 664-669, 1986 and Graham, Gastroenterology 96: 615-625, 1989).
The recognition that peptic ulcer is an infectious disease caused by the bacterium H. pylori has revolutionized the approach of diagnosis and therapy. H. pylori has been implicated in the etiology of chronic gastritis and peptic ulcer disease and also of gastric carcinoma and gastric mucosa associated lymphoid tissue lymphoma, if infection persists for a life time (Forman et al., Lancet, 343, 243-244, 1994). International agency for cancer research (IARC, USA), recently declared H. pylori to be a Group I carcinogen, a definite cause of human gastric cancers.
There are several patents that describe different methods to treat H. pylori infections. U.S. Pat. No. 5286492 describes the method of treatment of H. pylori with Triclosan. European patent no. 713392 describes the use of Clioquinol for treating H. pylori infections and related diseases. European patent no. 676199 describes the use of Trifloxacin or derivatives for the treatment of H. pylori infections. European patent no. 758245 describes the use of Spiramycin for treating gastrointestinal disorders caused by H. pylori. WIPO patent no. 9528929 describes the use of amino-N-oxide antimicrobials for use against H. pylori infections.
At present, the treatment of peptic ulcers with drugs like H.sub.2 -receptor antagonists, gastric acid, secretion inhibitors and mucosal protectants has been replaced partially or totally, by antibiotics/antimicrobials. Triple therapy regimen (Tetracycline, in combination with metronidazole and tripotassium dicitratobismuthate, TDB) has been found to be more effective than monotherapy, but patient compliance and drug resistance, further limits its applicability. Difficulties arise in the localization of the drug by conventional delivery systems, since they settle at the base of the stomach and are emptied along with gastric emptying. As a result, little amount of drug is delivered to the body or fundus of the stomach. Ecological niche of H. pylori due to the fact that it lies beneath the mucosal layers and develops rapid resistance to antibiotics (drug resistance towards the causative organism, originating either from the impermeability of the bacterial membrane envelope, or dye to production of .beta.-lactamases), could be cited as reasons for the ineffectiveness of monotherapy and triple therapy (in some part) regimen. Systemic administration followed by local secretion in the gastric juice has been considered as an option for drug delivery to bacterium. Unfortunately, only strong bases diffuse into the stomach and the antibiotics used in H. pylori treatment being weak acids and bases, fail to enter the acid environment. There have been only a few drug delivery systems described, in prior art, to overcome problems of drugs used to treat H. pylori infections. WO/9624341 describes an approach to formulate drugs such as TDB in a chewing gum base for delivery to dental plaques and oral localized delivery. But this is a non-specific delivery and is not specifically targeted to H. pylori cells and suffers from the disadvantages of non-specificity. Moreover, many unpleasant tasting drugs may not be suitable for chewing gum dosage forms.
It is therefore appreciated that there is a need of novel delivery system which can combat with the biochemical and physico-chemical challenges encountered at infectious site (i.e., gastric mucosa) vis-a-vis presenting the system to the target cell lines with the help of specific ligands for the cell surface cytoporter system. Liposomes, the lipid bound microscopic vesicles have been used for targeting of the drugs to various target sites like fungal cells and cancerous cells. A great deal of research has been made on the ligand directed liposomal systems, mainly based on antibody mediated and carbohydrate mediated liposomal interactions. These have revealed some of the conceptual aspects of the enhanced in vitro and in-vivo stability and targeting potential as compared to native liposomes. Liposomes anchored with target-specific monoclonal antibody as a ligand are guided towards the cell surface antigens.
In our invention, we have adopted another novel strategy based on carbohydrate specific glycoconjugate ligands i.e. lectins. Lectins are proteins or glycoproteins that are capable of binding monosaccharidos, oligosaccharides and glycoproteins with an enzyme like specificity. The lectinized liposomes selectively approach their respective receptors expressed on to the surface of target cells. These receptors are cytoportals identified to be glyco-sphingolipids and glyco-proteins.
The carbohydrates recognition groups on the surface of target cells suggest the application of carbohydrate epitopes as ligands for intracytoplasmic targeted drug delivery. The concept of polyvalency or multivalency, i.e., binding to a target site through multiple interactions, viz. sugar affinity and specificity of membrane lectins for glyco-conjugates could be proposed as composite mechanisms. Among the glyco-conjugate linands, glycolipids, sphingoglycolipids, glycoproteins, lectins and polysaccharides are widely investigated pilot molecules to selective interact with biofilms and deliver the contents to cellular interiors. Lectinized liposomes have been used for targeting to HeLa cells (Liautard et al., Biol. Int. Rep., 2, 1123-1137, 1985), glycophorin--A biofilms (Hutchinson et al., FEBS Lett. 234, 493-496, 1988), mouse embryo and transformed fibroblast (Bogdanor et al., Exp. Cel. Res., 181: 362-375, 1989), chicken erythrocyte (Carpenter et al., Anal. Biochem., 135: 151-155, 1983), and Streptococcus infection (Kaszuba et al., Biochem. Soc. Trans., 19: 4165, 1991). Lectin appended liposomes interact selectively with the sugars expressed on cell surface as glycoconjugates. The specificity of the lectins for binding to a particular sugar has been appreciated as site directing component or character. The targeting could be negotiated via carbohydrate mediated interactions.
The multivalency characteristics of lectins impart to it, selectivity and affinity for bacterial cells. Appended ligands [lectins like Concanavallin A (Con A), Wheat germ agglutinin (WGA) and Rat cerebellum agglutinin (RCA)] owing to their sugar affinity and specificities, specifically adhere to the glycocalyx of the bacterial biofilm. The composition as described in this invention system, thus may selectively deliver the drug not only to the bacterial cell proximity but also via receptor mediated uptake in to cellular interiors.
The approach as described in this invention therefore, would be utilized to circumvent ulcerative and carcinogenesis associated with H. pylori infections in the upper GIT, simultaneously to steric protection and confer structural integrity to the disintegrated mucosal cell lines. The novel composition as described in the present invention is based on liposomes constituted using WGA acylated Phosphatidyl ethanolamine (PE) as film forming lipid component. PE itself fails forming bilayers (which usually adopts the hexagonal inverted micelle structure in preference to bilayer sheet) however, on derivatization with palmitoyl or acyl WGA/antibiodies it may form stable vesicular constructs entrapping water soluble susbstanits. On partitioning of acylated WGA-PE through ligand-receptor clustering, the system destabilizes and the contents are instantaneouly released. The lectin serves for ligands and recognizes its affinity receptor expressed on to the bacterial films. This as a result could place liposome on bacterial film releasing its antibacterial contents. In addition, the lipid components may serve as prostaglandin precursors or stimulus offering cytoprotection via inflamed site biochemistry manipulation.